The invention is in the field of the packaging industry and relates to a closure unit and a production process for the same.
On containers for liquids, such as e.g. metal cans or coated cardboard receptacles, for the purpose of a resealable opening and easy pouting, closure units are often provided, which are preferably made from plastic and comprise a pouring part with a pouring opening and a closure part closing the pouring opening of the pouring part and which are fitted in an opening of the container. The two Swiss patent applications 2740/91 and 2739/91 (application date 17.9.91) of the same Applicant describe such closure units. The described closure units are moulded according to a multimaterial injection moulding process and comprise at least two materials differing with respect to at least one characteristic.
In application 2740/91, it is required for problem-free transportation that the closure unit is constructed in such a way that, prior to the first opening, it can withstand without damage a rough transportation process, but can still be opened the first time with little force expenditure. As an additional securing feature for the new state a predetermined breaking point between the pouring part and the closure part is proposed, which is broken open at the first opening. This predetermined breaking point passes between the closure part and the pouring part around at least a portion of the pouring opening circumference and namely in an area made from one material extending in the closure part and the pouting part. It is a linear zone, in which the material is very thin.
Known closure units moulded from one material can also have such predetermined breaking points. Such closure units are moulded in a pseudo-closed state, i.e. the closure part is shaped by means of a predetermined breaking point onto the pouting part. During the first opening the closure part is separated from the pouring part along the predetermined breaking point. As the broken predetermined breaking point is not adequate as a sealing surface on resealing during the latter operation the closure part must be brought into a further closed state, which mainly consists of the closure part being forced more deeply over the pouring part. In the new state (pseudo-closed state) the predetermined breaking point is located directly on the outer surface of the closure unit and constitutes an easily damageable point.
The object of the invention is to provide a closure unit which, in the new state is additionally secured by a predetermined breaking point between the pouring part and the closure part, but whose closed state is the same when new and when resealed (no pseudo-closed state) and which in the reseated state is sealed by sealing surfaces and not sealing edges. The predetermined breaking point is improved compared with known predetermined breaking points with respect to its exposability, its sensitivity to forces directed differently to the forces required for closure unit opening and/or with regards to aids enabling the predetermined breaking point to be precisely positioned and to limit the force required for breaking it open.
The inventive closure unit is produced according to a multimaterial injection moulding procedure from at least two thermoplastic materials, which differ as regards at least one characteristic. At least one area consisting of one of the materials extends from the pouring part into the closure part and can form a predetermined breaking point at the transition. To the area having the predetermined breaking point is advantageously on the outside of the closure unit closely fitted an area made from a different material, which as a protection/support zone extends beyond the predetermined breaking point and is advantageously firmly connected on the closure part-side of the predetermined breaking point to the area having the latter, whereas on the pouting part-side of the predetermined breaking point it adheres either not at all or only very slightly to the area having said point, so that in the area between the pouring part and the closure part a separable sealing surface pair is formed.
The described protection/support zone can also be located on the inside of the closure unit, but can then only fulfil a very limited protection function.
The described outer protection/support zone can be supplemented by an identical protection/support zone on the inside of the closure unit or by one or two support zones, which on the pouting part side and/or closure part side closely fit and are firmly connected to the area having the predetermined breaking point and extend as close as possible to but do not extend over said point.
As a result of the described protection/support zones and support zones the predetermined breaking point is protected against damage and supported in such a way that it cannot be broken open by external pressure on the closure part, by pressure in the interior of the container or by forces acting laterally on the closure unit.
If the inventive closure unit has a hinge as a permanent connection between the closure part and the pouring part, and if this hinge forms part of the wall of the pouring opening, the predetermined breaking point extends only partly round the pouring opening circumference. If the hinge is positioned outside the pouring opening or if the closure unit does not have any connecting means between the pouting part and the closure part, the predetermined breaking point extends all around said opening.
If the hinge consists of a thin material area pivotally connecting the closure part and the pouting part, this area forms a continuation of the predetermined breaking point, such that the predetermined breaking point and the thin material zone form a closed line around the pouring opening. In order to prevent an extension of the predetermined breaking point into the thin connecting zone by propagation of cracks when the predetermined breaking point is broken or when the closure unit is reopened, special precautions must be taken at the end zones of the predetermined breaking point.
The area comprised of one material which extends from the pouring part into the closure part and in which the predetermined breaking point is located, may be such shaped that it covers, at least in the closed state of the closure unit the whole inner surface of the latter. This is advantageous if the goods to be stored are only compatible with one of the materials of which the closure unit is made. For such a closure unit it is only possible to provide a protection/support zone on the outside.